Merge branch 'master' into qt4-tag

Author: dcwhite

src/Externals/spire/arc-ball/ArcBall.cpp

@@ -60,7 +60,7 @@ void ArcBall::drag(const glm::vec2& msc)
   glm::vec3 mVSphereNow = mouseOnSphere((mScreenToTCS * glm::vec4(msc, 0.0, 1.0)).xyz());
 
   // Construct a quaternion from two points on the unit sphere.
-  glm:: quat mQDrag = quatFromUnitSphere(mVSphereDown, mVSphereNow);
+  glm::quat mQDrag = quatFromUnitSphere(mVSphereDown, mVSphereNow);
   mQNow = mQDrag * mQDown;
   if(glm::dot(mVSphereDown, mVSphereNow) < 0.0)
     beginDrag(msc);
@@ -77,9 +77,14 @@ void ArcBall::setLocationOnSphere(glm::vec3 location, glm::vec3 up)
 glm::quat ArcBall::quatFromUnitSphere(const glm::vec3& from, const glm::vec3& to)
 {
   glm::vec3 axis = glm::normalize(glm::cross(from, to));
+
+  // Give arbitrary non-zero vector because no rotation
+  if (std::isnan(axis[0]))
+    axis = from;
+
   float angle = std::acos(glm::dot(from, to));
 
-  if(angle <= 0.00001)
+  if(angle <= 0.00001 || std::isnan(angle))
     return glm::quat(1.0, 0.0, 0.0, 0.0);
 
   return glm::angleAxis(angle, axis);